Synergistic antimicrobial composition

ABSTRACT

A synergistic antimicrobial composition comprising:
         (a) a hydroxymethyl-substituted phosphorus compound selected from the group consisting of tetrakis(hydroxymethyl)phoshponium salts and tris(hydroxymethyl)phosphine; and   (b) tris(hydroxymethyl)nitromethane.

This invention relates to combinations of biocides, the combinationshaving greater activity than would be observed for the individualantimicrobial compounds.

Use of combinations of at least two antimicrobial compounds can broadenpotential markets, reduce use concentrations and costs, and reducewaste. In some cases, commercial antimicrobial compounds cannot provideeffective control of microorganisms, even at high use concentrations,due to weak activity against certain types of microorganisms, orrelatively slow antimicrobial action, or instability under certainconditions such as high temperature and high pH. Combinations ofdifferent antimicrobial compounds are sometimes used to provide overallcontrol of microorganisms or to provide the same level of microbialcontrol at lower use rates in a particular end use environment. Forexample, U.S. Pat. No. 5,385,896 discloses combinations of phosphoniumsalts and aldehydes, but this reference does not suggest any of thecombinations claimed herein. Moreover, there is a need for additionalcombinations of antimicrobial compounds having enhanced activity toprovide effective control of microorganisms. The problem addressed bythis invention is to provide such combinations of antimicrobialcompounds.

STATEMENT OF THE INVENTION

The present invention is directed to a synergistic antimicrobialcomposition comprising: (a) a hydroxymethyl-substituted phosphoruscompound selected from the group consisting oftetrakis(hydroxymethyl)phoshponium salts andtris(hydroxymethyl)phosphine; and (b) tris(hydroxymethyl)nitromethane(Tris Nitro); wherein a weight ratio of the hydroxymethyl-substitutedphosphorus compound to tris(hydroxymethyl)nitromethane is from 8:1 to1:12.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the following terms have the designated definitions,unless the context clearly indicates otherwise. The term “antimicrobialcompound” refers to a compound capable of inhibiting the growth orpropagation of microorganisms, and/or killing microorganisms;antimicrobial compounds include bactericides, bacteristats, fungicides,fungistats, algaecides and algistats, depending on the dose levelapplied, system conditions and the level of microbial control desired.The term “microorganism” includes, for example, fungi (such as yeast andmold), bacteria and algae. The following abbreviations are usedthroughout the specification: ppm=parts per million by weight(weight/weight), mL=milliliter, Unless otherwise specified, temperaturesare in degrees centigrade (° C.), and references to percentages are byweight (wt %). Percentages of antimicrobial compounds in the compositionof this invention are based on the total weight of active ingredients inthe composition, i.e., the antimicrobial compounds themselves, exclusiveof any amounts of solvents, carriers, dispersants, stabilizers or othermaterials which may be present. The hydroxymethyl-substituted phosphoruscompound is selected from the group consisting oftetrakis(hydroxymethyl)phosphonium salts (e.g.,tetrakis(hydroxymethyl)phosphonium sulfate (THPS) andtetrakis(hydroxymethyl)phosphonium chloride) andtris(hydroxymethyl)phosphine. More than one hydroxymethyl-substitutedphosphorus compound may be present, in which case the biocide ratio iscalculated from the total content of such compounds.

In some embodiments of the invention, a weight ratio of thehydroxymethyl-substituted phosphorus compound(s) totris(hydroxymethyl)nitromethane is from 7:1 to 1:12, alternatively from8:1 to 1:9, alternatively from 7:1 to 1:9, alternatively from 7:1 to1:8, alternatively from 6:1 to 1:12, alternatively from 6:1 to 1:10,alternatively from 6:1 to 1:9, alternatively from 6:1 to 1:8;alternatively from 5:1 to 1:12, alternatively from 5:1 to 1:10,alternatively from 5:1 to 1:9, alternatively from 5:1 to 1:8;alternatively from 4:1 to 1:12, alternatively from 4:1 to 1:10,alternatively from 4:1 to 1:9, alternatively from 4:1 to 1:8;alternatively from 3:1 to 1:12, alternatively from 3:1 to 1:9,alternatively from 3:1 to 1:10, alternatively from 3:1 to 1:8. In someembodiments of the invention, the composition is used to preventmicrobial growth in a medium at higher temperatures and high sulfidelevels, i.e., at least 50° C. and 2 ppm sulfide, conditions whichtypically are present in oil and gas wells and reservoirs. In theseembodiments, the weight ratio of the hydroxymethyl-substitutedphosphorus compound to tris(hydroxymethyl)nitromethane is from 1:1.5 to1:12; alternatively from 1:1.5 to 1:10; alternatively from 1:1.5 to 1:9;alternatively from 1:1.5 to 1:8; alternatively from 1:1.8 to 1:12;alternatively from 1:1.8 to 1:10; alternatively from 1:1.8 to 1:9;alternatively from 1:1.8 to 1:8; alternatively from 1:2 to 1:12;alternatively from 1:2 to 1:10; alternatively from 1:2 to 1:9;alternatively from 1:2 to 1:8. In some embodiments of the invention, ahigher temperature and high-sulfide medium is one having a temperatureat least 60° C. and a sulfide level at least 4 ppm. In some embodiments,the temperature is at least 65° C.; alternatively at least 70° C.;alternatively at least 75° C.; alternatively at least 80° C. In someembodiments, the medium contains at least 5 ppm sulfide, alternativelyat least 6 ppm sulfide, alternatively at least 7 ppm sulfide,alternatively at least 8 ppm sulfide, alternatively at least 9 ppmsulfide, alternatively at least 10 ppm sulfide. In some embodiments ofthe invention, the medium to which the antimicrobial composition isadded is anaerobic. In some embodiments of the invention, the anaerobicmedium is a high-temperature and high-sulfide environment. In someembodiments of the invention, the medium to which the antimicrobialcomposition is added contains sulfate-reducing bacteria. In someembodiments of the invention, the high-temperature and high-sulfideenvironment contains sulfate-reducing bacteria. In some embodiments ofthe invention, the medium to which the antimicrobial composition isadded is an aqueous medium, i.e., one comprising at least 60% water,alternatively at least 80% water. In some embodiments of the invention,the aqueous medium is a high-temperature and high-sulfide medium.

In some embodiments of the invention, the antimicrobial combination ofthis invention is useful in oil and gas field injection, producedfluids, fracturing fluids and functional fluids, oil and gas wells, oiland gas operation, separation, storage, and transportation systems, oiland gas pipelines, oil and gas vessels, and fuel. The combination isespecially useful in aqueous fluids added to or produced by oil and gaswell. The composition also is useful for controlling microorganisms inother industrial water and water containing/contaminated matrixes, suchas cooling water, air washer, heat exchangers, boiler water, pulp andpaper mill water, other industrial process water, ballast water,wastewater, metalworking fluids, latex, paint, coatings, adhesives,inks, tape joint compounds, pigment, water-based slurries, personal careand household products such as detergent, filtration systems (includingreverse osmosis and ultrafiltration systems), toilet bowel, textiles,leather and leather production system, or a system used therewith.

Typically, the amount of the biocide combinations of the presentinvention to control the growth of microorganisms is from 10 ppm to5,000 ppm active ingredient. In some embodiments of the invention, theactive ingredients of the composition are present in an amount of atleast 20 ppm, alternatively at least 50 ppm, alternatively at least 100ppm, alternatively at least 150 ppm, alternatively at least 200 ppm. Insome embodiments, the active ingredients of the composition are presentin an amount of no more than 2,000 ppm, alternatively no more than 1,000ppm, alternatively no more than 500 ppm, alternatively no more than 400ppm, alternatively no more than 300 ppm, alternatively no more than 250ppm, alternatively no more than 200 ppm, alternatively no more than 100ppm, alternatively no more than 50 ppm. Concentrations mentioned aboveare in a liquid composition containing the biocide combinations. Biocideconcentrations in a high-sulfide and high-temperature environmenttypically will be higher than in other environments.

The present invention also encompasses a method for reducing, orinhibiting, or preventing microbial growth in the use areas describedabove, especially in oil or natural gas production operations, byincorporating the claimed biocide combination into the materials.

EXAMPLES Example 1 Synergistic Effect of THPS and Tris Nitro againstSulfate Reducing Bacteria (SRB)

Inside an anaerobic chamber (BACTRON anaerobic chamber), a deaeratedsterile salt solution (3.1183 g of NaCl, 1.3082 mg of NaHCO₃, 47.70 mgof KCl, 72.00 mg of CaCl₂, 54.49 mg of MgSO₄, 172.28 mg of Na₂SO₄, 43.92mg of Na₂CO₃ in 1 L water) was contaminated with an oil field isolatedanaerobic consortium, mainly SRB, at final bacterial concentrations of10⁶ to 10⁷ CFU/mL. The aliquots of this contaminated water were thentreated with THPS and Tris Nitro, or the THPS/Tris Nitro combination atdifferent active concentration levels. After the mixtures were incubatedat 40° C. for 24 hours, the biocidal efficacy was determined by minimumtested biocide concentration for bacteria kill in the aliquots (MBC).Table 1 summarizes the efficacy of each biocide and their blends, andthe Synergy Index* of each combination.

TABLE 1 Biocidal efficacy of THPS, Tris Nitro, THPS/Tris Nitrocombination, and Synergy Index Average MBC Ratio of THPS to (active ppm)Average p value Tris Nitro (active Tris Synergy in w/w) THPS NitroIndex*¹ ztest*² 1:0 6.1 0.0 9:1 6.0 0.7 1.02 0.66 3:1 4.9 1.6 0.87 0.001:1 4.4 4.4 0.84 0.00 1:3 3.8 11.5 0.90 0.03 1:9 2.5 22.6 0.93 0.08 0:10.0 46.1 *¹Synergy Index = Ca/CA + Cb/CB Ca: Concentration of biocide Arequired to achieve a certain level of bacterial kill when used incombination CA: Concentration of biocide A required to achieve a certainlevel of bacterial kill when used alone Cb: Concentration of biocide Brequired to achieve a certain level of bacterial kill when used incombination CB: Concentration of biocide B required to achieve a certainlevel of bacterial kill when used alone *²P value < 0.05 means thatthere is significant difference between the average Synergy Index and1.00

Example 2 Evaluation of Biocidal Efficacy of THPS, Tris Nitro, and TheirCombination against Anaerobic Bacteria for a High Temperature andSulfide-Rich Environment

Inside an anaerobic chamber (BACTRON IV), biocides solutions werechallenged with 10⁴ to 10⁵ CFU/mL of an oilfield SRB consortium and 10ppm sulfide ion (added in the form of sodium sulfide). The biocidesolutions were then incubated at 80° C. under anaerobic condition for 7days. Then the biocidal efficacy was evaluated against the field SRBconsortium. The biocidal efficacy was determined by the biocide dosagerequired for 99.999% bacterial reduction. Synergy Index was thencalculated. Table 2 summarizes the efficacy of each biocide and theirblends, and the Synergy Index* of each combination.

TABLE 2 Biocidal efficacy evaluation of THPS, Tris Nitro, and THPS/TrisNitro combination for a high temperature and sulfide-rich environment,and Synergy Index Concentration (active ppm) required for 99.999%bacterial Ratio of THPS to Tris reduction (active ppm) Synergy Nitro(active w/w) THPS Tris Nitro Index 1:0 360.0 0.0 2:1 >180 >90 >0.751:1 >180 >180 >1 1:2 90 180 0.75 1:4 45 180 0.63 1:8 22.5 180 0.56 0:1 0360

Table 2 shows that the THPS and Tris Nitro combination was synergisticfor a high temperature and sulfide-rich environment.

1. A synergistic antimicrobial composition comprising: (a) ahydroxymethyl-substituted phosphorus compound selected from the groupconsisting of tetrakis(hydroxymethyl)phoshponium salts andtris(hydroxymethyl)phosphine; and (b) tris(hydroxymethyl)nitromethane;wherein a weight ratio of the hydroxymethyl-substituted phosphoruscompound to tris(hydroxymethyl)nitromethane is from 8:1 to 1:12.
 2. Thecomposition of claim 1 in which the weight ratio is from 5:1 to 1:10. 3.The composition of claim 2 in which the hydroxymethyl-substitutedphosphorus compound is tetrakis(hydroxymethyl)phosphonium sulfate. 4.The composition of claim 3 in which the weight ratio is from 4:1 to 1:9.5. The composition of claim 4 in which. the weight ratio is from 3:1 to1:8.
 6. A method for inhibiting microbial growth in a medium at atemperature of at least 60° C. and a sulfide level at least 4 ppm; saidmethod comprising adding to the medium: (a) a hydroxymethyl-substitutedphosphorus compound selected from the group consisting oftetrakis(hydroxymethyl)phoshponium salts andtris(hydroxymethyl)phosphine; and (b) tris(hydroxymethyl)nitromethane;wherein a weight ratio of the hydroxymethyl-substituted phosphoruscompound to tris(hydroxymethyl)nitromethane is from 1:1.5 to 1:12. 7.The method of claim 6 in which the temperature is at least 70° C. and asulfide level at least 7 ppm; and in which said weight ratio is from1:1.8 to 1:10.
 8. The method of claim 7 in which thehydroxymethyl-substituted phosphorus compound istetrakis(hydroxymethyl)phosphonium sulfate.
 9. The method of claim 8 inwhich the medium is anaerobic and contains sulfate-reducing bacteria.10. The method of claim 9 in which said weight ratio is from 1:2 to 1:8.